Field Project in Mali, West Africa Throughout most of sub-Saharan Africa, the assumption is that if a patient has an acute febrile, recurring disease, the patient has, and is treated for, malaria. This would explain many treatment failures if the patients had relapsing fever, as the drugs used to treat malaria are ineffective against relapsing fever spirochetes. Malaria is highly prevalent and a serious human infection in Mali, where NIAID has ongoing projects on malaria and leishmaniasis, both vector-borne infections. Little is known about tick-borne relapsing fever in Mali, but given its prevalence in nearby Senegal, and two observations regarding spirochetes in patients in western Mali (Rodhain et al., 1991, Bull. Soc. Path. Ex. 84:30-45), we believe relapsing fever may be significantly misdiagnosed as malaria, as we found recently in Togo (Nordstraand, et al. Tickborne relapsing fever diagnosis obscured by malaria, Togo. Emerging Infect. Dis. 13: 117-123, 2007). The goal of this project is to evaluate the potential for human tick-borne relapsing fever in Mali. Our efforts will be directed at capturing small mammals and testing their blood for spirochetes and antibodies specific for relapsing fever infections;collecting ticks and testing them for spirochete infection;and testing human serum samples already collected for other studies to detect the presence of relapsing fever antibodies. Tick-borne relapsing fever caused by B. crocidurae in West Africa is also a zoonosis, and in Senegal small rodents and shrews are the primary enzootic vertebrate hosts for the spirochete and ticks in nature. Most people become infected with B. crocidurae while sleeping in tick-and rodent-infested huts, as described for a longitudinal study in Senegal published recently (Vial et al., 2006, Incidence of tick-borne relapsing fever in West Africa;longitudinal study, Lancet 368:37-43). The soft tick vector, Ornithodoros sonrai, is nocturnal and feeds quickly in 15 to 60 minutes, so most people are unaware of having been bitten (quite similar to the situation in western North America).